The present invention relates to a surface grinding machine and a surface grinding method for through-feed grinding workpieces by the through-feed grinding method, adapted to reduce the number of defectively ground articles produced during the through-feed grinding and to reduce wear in grinding stones.
Concerning two-sided surface grinding machines for surface-grinding workpieces by the through-feed grinding method, many techniques have already been proposed, including Patent Document 1 (Japanese Patent Laid-Open No. Hei 5-8161), and Patent Document 2 (Japanese Patent Laid-Open No. 2005-329522). Such two-sided surface grinding machine is adapted to simultaneously grind the opposite surfaces of workpieces, by the through-feed grinding method, held by a carrier and received in pockets circumferentially formed in said carrier by feeding said workpieces between a pair of grinding stones rotating around the axes of spindles.
Concerning devices for simultaneously finish-grinding the opposite surfaces of workpieces, there is one in which, as in the invention disclosed in Patent Document 3 (Japanese Utility Model Laid-Open No. 63-124461), for example, on the front ends of a pair of coaxially disposed spindles are mounted opposed grinding stones floatably in all directions, said pair of grinding stones simultaneously finish-grinding the opposite surfaces of workpieces.
As for two-sided surface grinding machines, they have heretofore been provided with various measures for securing the rigidity of the spindle units including spindles, the main frame, and the like so as to sufficiently withstand the grinding loads during the workpiece grinding. However, it is impossible to fully prevent the axial displacements, in the escape direction, of the grinding stones caused by the grinding loads.
Thus, analyzing the through-feed grinding state reveals that during the continuous processing of workpieces, the grinding load is so heavy as to produce given axial displacements, in escape direction, of the grinding stones, but immediately before the end of the continuous processing, the grinding loads so sharply decrease that the axial displacements disappear. Therefore, depending on the presence or absence of such axial displacement, the spacing between the pair of grinding stones makes a delicate change on the exit side of workpieces, so that the thickness of the workpieces processed in the last stage tends to be small.
Further, in the device described in Patent Document 3, the grinding stones tilt in all directions but the grinding stones only follow the surfaces to be ground of the workpieces. Therefore, even if the techniques shown in Patent Document 3 are applied to a two-sided surface grinding machine, the front ends of the grinding stones follow the workpieces only to float, and a reduction in the number of defectively ground articles produced by the through-feed grinding or improvements in the precision of workpiece processing cannot be expected.
In view of these problems in prior art, an object of the invention is to provide a surface grinding machine, a spindle device, and a surface grinding method capable of reducing the number of defectively ground articles produced by the through-feed grinding and capable of reducing wear in grinding stones.